Look at this semi-lunar black shadow. It is called finger-nail artifact. But is it due to finger-nail impression on the film? If so, then the radiographer or technician must have a very long finger nail to do that.
Actually, it is due to improper handling of the unexposed film. This happens in the darkroom during loading of the film into the cassette. While holding at the side, the film in the middle becomes bent and causes the semi-lunar impression.